Biofuel production via microalgal systems can produce a wide range of feedstocks for transformation into biodiesel, bioethanol, biomethane and biohydrogen (FIG. 1). Microalgae can be cultivated in non-food producing environments such as deserts and oceans and may utilize fresh, saline or waste water streams in conjunction with CO2-producing power and industrial plants for fixing carbon and reutilizing phosphates and nitrates.
Lipid molecules are stored inside small spherical structures inside microalgal cells called vesicles. In order to access the contents of the vesicles the cell wall must be disturpted or lysed. Disruption creates holes in the cell wall, resulting in the partial release of contents. Lysis results in the complete release of contents.
Consequently, complete or nearly complete destruction or removal of the cell wall is critical. Microalgal cell walls contain cellulose, which make their complete lysis by organic solvents alone difficult or impossible. In addition, vesicle walls are made of lipid mono-Ibilayers, which must also be disrupted or lysed, but are susceptible to chemical lysis by organic solvents and aqueous detergents. Because chemical lysis requires costly and/or toxic chemicals that must be separated from the desired products, cell concentrates are usually lysed nonchemically using one or more of high-pressure homogenization, supercritical fluid homogenization, electroporation, and radiation, all of which are energy-intensive because of the dissipative effects of the intervening aqueous media. Lipids are then usually removed from the cell lysate via distillation.
Current methods for harvesting microalgae and extracting biofuels and other lipids from the harvested microalgae also involve one or more processes that concentrate algae cells. Microalgae cell concentration is often inefficient because the cells possess physical properties that are similar to the suspending aqueous medium, including similar density, magnetic susceptibility, and refractive index.